(1) Field of the Invention
The present invention relates to a water-in-oil emulsion explosive composition (hereinafter, abbreviated as W/O emulsion explosive composition), and more particularly relates to a W/O emulsion explosive composition having a remarkably improved storage stability in initiation sensitivity in small diameter cartridges and at low temperatures, which does not contain explosives, non-explosives, detonation-catalytic sensitizers or sensitive oxidizers, such as chlorate, perchlorate or the like of ammonium or alkali metal, used in conventional W/O emulsion explosive compositions for improving their initiation sensitivity, but contains a specifically limited weak acid salt or a specifically limited condensed phosphate.
(2) Description of the Prior Art
There have hitherto been known a large number of W/O emulsion explosive compositions having an improved initiation sensitivity in small diameter cartridges and at low temperatures, which contain an explosive sensitizer, such as nitroglycerine or the like, a non-explosive sensitizer, such as monomethylamine nitrate or the like (hereinafter, the above described explosive and non-explosive sensitizers are referred to as sensitive substances), a detonation-catalytic sensitizer, such as a compound of metals having an atomic number of at least 13 and being other than the metals of Groups I and II in the Periodic Table, a water-soluble strontium compound or the like, or a sensitive oxidizer, such as perchlorate or the like of ammonium or alkali metals (hereinafter, the above described detonation-catalytic sensitizer and sensitive oxidizer are referred to as auxiliary sensitive substances). However, in the production of these W/O emulsion explosive compositions, the above described sensitive substance or auxiliary sensitive substance must be transported and compounded, and are very dangerous in handling. Moreover the volatile gas generated during the production of the explosive compositions and the explosion gas generated after the use of the explosive compositions are often uncomfortable and toxic. Furthermore, the raw materials for the explosive compositions are often expensive. Accordingly, it is desirable to produce explosive compositions containing neither sensitive substances nor auxiliary sensitive substances. Under these circumstances, some W/O emulsion explosive compositions have hitherto been proposed, which do not contain the above described sensitive substances or auxiliary sensitive substances, but can be detonated in the state of a small diameter cartridge by a No. 6 or No. 8 blasting cap.
For example, U.S. Pat. No. 4,110,134 discloses that a W/O emulsion explosive composition containing glass microballoons as a gas-retaining agent can be completely detonated up to a density of maximum 1.25 in a cartridge diameter of about 1.25 inches (31.8 mm) by a No. 6 blasting cap. Further, U.S. Pat. No. 4,149,917 discloses that a W/O emulsion explosive composition, whose density has been adjusted to 0.95 by introducing microbubbles into the explosive composition without the use of gas-retaining agent, is completely detonated (explosive temperature: 21.1.degree. C.) in a cartridge diameter of 1.25 inches (31.8 mm) by a No. 6 blasting cap even after a lapse of time of 2 months from the production of the explosive composition, and further is completely detonated (explosive temperature: 21.1.degree. C.) in a cartridge diameter of 1.25 inches (31.8 mm) by a No. 8 blasting cap after a lapse of time of 8 months from the production of the explosive composition.
Conventional W/O emulsion explosive compositions not containing the above described sensitive substances or auxiliary sensitive substances are completely detonated in a small cartridge diameter of 1.25 inches by a No. 6 blasting cap or a No. 8 blasting cap, but still have drawbacks that the explosive compositions are insufficient in initiation sensitivity in a cartridge diameter smaller than 1.25 inches and at low temperature, and in storage stability in its initiation sensitivity.
The inventors have made various investigations in order to obviate the above described problems in the initiation sensitivity in a small cartridge diameter (for example, 1 inch) and at a low temperature of -5.degree. C. and in the storage stability in its initiation sensitivity, and have thereby accomplished the present invention.